The present invention relates to a coarse adjusting deice of a scanning tunneling microscope and, more particularly, to a coarse adjusting device having a mechanical transmission mechanism.
In general, a scanning tunneling microscope has a coarse adjusting device and a fine adjusting device which are arranged in a pair. A specimen to be observed is held by a coarse adjusting device, while a probe is provided on the fine adjusting device. In operation, the coarse adjusting device first operates to bring the surface of the specimen to a position near the end of the probe, e.g., to a position which is about 0.1 mm away from the end of the probe. Then, the fine adjusting device operates so as to bring the probe closer to the surface of the specimen, while applying a predetermined voltage between the specimen and the probe, until the tunnel current flowing between the specimen and the probe reaches a predetermined level. Subsequently, the fine adjusting device operates to enable the probe to scan the surface of the specimen so that any concavities and convexities on the specimen surface are sensed and determined in atomic scale through the detection of the change in the tunnel current.
The known coarse adjusting devices are generally sorted into the following groups:
(1) piezoelectric coarse adjusting device [G. Binnig and H. Rohror Surface Science., Vol. 126 pp 236-244 (1983)] PA0 (2) magnetic coarse adjusting device [D. P. E. Smith and S. A. Elrod: Rev. Sci. Instrum., Vol. 56 pp 1970-1971 (1985), B. W. Corb, M. Ringger and H. J. Guntherrodt: J. Appl. Phys., Vol. 58 pp 3947-3953 (1985)] and PA0 (3) mechanical coarse adjusting device [J. E. Demuth, R. J. Hamers, R. M. Tromp and M. E. Welland: J. Vac. Sci. Technol., Vol. A4(3) pp 1320-1323 (1968)]
The piezoelectric coarse adjusting mechanism employs a piezoelectric element both ends of which are alternately fixed by electrostatic attraction. The coarse adjustment is effected by causing the piezoelectric element to expand or to contract. This type of device suffers from a disadvantage in that a drift of atomic scale is caused in the electrostatic attraction so as to impair smooth movement.
The magnetic coarse adjusting mechanism incorporates a permanent magnet and a solenoid coil which cooperate with each other in effecting the fixing and movement by magnetic forces. This type of coarse adjusting mechanism, however, is not suitable for use with the scanning electron microscope because the operation of the microscope tends to be adversely affected by the static magnetic field produced by the permanent magnet. In addition, this type of device shows an inferior mechanical rigidity because the fixing is effected by magnetic force.
The mechanical coarse adjusting device employ cantilevered thin plates carrying a probe and a specimen. The free ends of the plates are urged by for example, screws or springs so as to effect relative movement of the object such as the specimen. In this case, the amount of movement of the screw or the spring directly provides the displacement of the object, so that it is very difficult to effect a fine and smooth movement of the object.